The invention relates generally to conveyorized transport systems and deals more particularly with a system for tracking carriers in a computer controlled carrier and rail network.
Trolley and rail networks were previously known which utilize a main rail to guide workpiece carrying trolleys to subsidiary loops located along the main rail, each subsidiary loop leading to and from an associated work station. By way of example, the workpieces may be garments and the work stations may be sewing stations.
A sensor may be provided adjacent to a loading region of the main rail to read codes on the trolleys as the trolleys are loaded, and an operator may enter data into a computer to indicate the type of workpieces which the trolleys carry. Then the computer schedules the trolleys to proceed to various ones of the work stations. By controlling a means for driving the trolleys and the switches, the computer usually knows the approximate locations of the trolleys. However, occasionally a trolley falls off the main rail or subsidiary loops or is intentionally removed from them and not immediately returned to the proper rail or returned to a different location relative to the driving means. In addition, a new carrier may be added to the main rail or subsidiary loops. In which cases, it is important that the computer soon learns of the change to trolley location, its absence, or the presence of the new carrier.
In one previously known trolley and rail network, two switches are provided between the main rail and each subsidiary loop. One switch is located at the upstream end of the subsidiary loop relative to the direction of travel of the trolleys along the main rail to divert a trolley and the workpieces it carries from the main rail to the subsidiary loop and another switch is located at the downstream end of the subsidiary loop to return the trolley to the main rail. Additional trolley code sensors are located along the main rail immediately upstream of the switches which divert the trolleys from the main rail to the subsidiary loops to periodically inform the computer of the location of the trolleys so that the computer can update its tracking information as needed. A drawback to this arrangement of switches and sensors is that the trolley codes may only be read on their way into a subsidiary loop (or past it if it bypasses the subsidiary loop) and if a trolley is misplaced in a loop or removed from it, the computer will not learn of the event until the time that the trolley was scheduled to approach the next take-off switch. If additional sensors were installed after the return switches this would add to the cost and complexity of the tracking system.
Another type of trolley and rail network is disclosed in U.S. Pat. Application Ser. No. 683,379 filed Dec. 19, 1984 by Harold Osthus and Roald Nymark, assigned to the assignee of the present invention and hereby incorporated by reference as part of the present disclosure. This type of trolley and rail network includes a main rail and paired and unpaired subsidiary loops located along the main rail, each subsidiary loop leading to and from a work station. The subsidiary loops of each pair are located on opposite sides of the main rail directly across from one another. The network also includes a switching means for each pair of subsidiary loops or each unpaired subsidiary loop for transferring a trolley between the main rail and the subsidiary loops. Each of the subsidiary loops has an entrance and an exit, the entrance being located downstream of the exit relative to the general direction of trolley movement on the main rail. The switching means transfers a carrier from the main rail to the entrance of the associated subsidiary loop and later receives the carrier from the exit of the loop. This switching means and subsidiary loop configuration provides flexibility in routing; a trolley may be routed in three different ways from the exit of each paired subsidiary loop or in two ways from the exit of each unpaired subsidiary loop. At the exit of a paired subsidiary loop, the trolley can be routed back to the main rail for movement downstream to another subsidiary loop, across the main rail to the other subsidiary loop of the pair or from the discharge end of one subsidiary loop directly to the entrance of the same subsidiary loop for recirculation purposes. The computer may initiate the recirculation for a variety of reasons, for example, to rearrange the ordering of the trolleys so that one work operation may be performed before another work operation or so that garments which require sewing by a particular type or color of thread may be grouped together.
Trolleys in this second type of trolley and rail network may be outfitted with machine readable codes as in the first type of trolley and rail network to identify the trolleys, and when the trolleys are initially loaded onto the main rail, an operator may enter into the computer the type of garments or other workpieces which are carried by the trolleys. Then, the computer directs the movements of the trolleys along the network. As in the first type of trolley and rail network, occasionally trolleys are removed from the network or become misplaced. Often several trolleys collect in a subsidiary loop while they await attention by an operator and because of the physical contact there between the operator and the trolleys and workpieces they carry, a trolley may be inadvertently knocked off the subsidiary loop rail, and either be left unnoticed or be replaced at the wrong location relative to the other trolleys in the subsidiary loop. Under these conditions, if one or more of the trolleys in the subsidiary loop is scheduled for recirculation or transfer to the opposite subsidiary loop, scheduling errors may occur.
Accordingly, a general object of the present invention is to provide in a conveyorized transport system of the type in which coded workpiece carriers are routed by a switching means from a main rail to an entry end of a subsidiary loop and then returned to the switching means via a discharge end of the subsidiary loop, the entry end of the subsidiary loop being located downstream of the discharge end relative to the general direction of carrier movement on the main rail; a tracking means for reading the code on a carrier as it proceeds into and out of the subsidiary loop.
A more specific object of the tracking means of the foregoing type is to require only one sensor per subsidiary loop or pair of subsidiary loops, which subsidiary loops of each pair being located directly across the main rail from each other.
Another specific object is to provide a conveyorized transport system having a tracking means of the foregoing type which will detect errors in trolley location before a trolley which exits from one subsidiary loop is transferred downstream of the subsidiary loop, recirculated within the same subsidiary loop or transferred to an opposite subsidiary loop located across the main rail from the aforesaid subsidiary loop.